A laboratory colony of S. macroura, founded by three females and four males, was maintained over four breeding seasons. Reproductive success was high and four generations were produced before the colony was disbanded. Descendants of these animals are still breeding in another laboratory 11 years after the founding of the colony. A detailed prescription for the maintenance and management of a breeding colony is given. The animals bred between June and February, most females first entering oestrus in the early months of the season, in July or August. Female young born early in the season (before mid-October) matured in the season of their birth at an age of 86-159 days; those born later matured in the following season at an age of 185-262 days. In each group, those born later matured earlier. Minimum body weight at sexual maturity was 12.5 g. At least two litters can be reared in a season and individuals may breed in more than one season. S. macroura is polyoestrous with a mean cycle length of 23.25 days. The gestation period is about 11 days and up to eight young can be accommodated in the pouch. Lactating females may return to oesrrus up to 10 days before the young are weaned at 70 days old. Ovulation occurs spontaneously and the mean number of corpora lutea formed was 20.7. The corpora lutea reach maximal size late in pregnancy and they regress more rapidly in lactating than in non- lactating females. Up to three generations of corpora lutea could be recognised in the ovaries of females undergoing cycles uninterrupted by lactation. Changes In body weight, the pouch, and the gross and histological appearance of the reproductive tract were the same in pregnant and pseudopregnant females.